OBJECTIVES: (1) By tetrad analysis, we shall test a model for gene conversion in fungi proposed (by C.M. Radding) to explain parity in the conversion of deletion mutations. (2) By transformation, we shall introduce Chi elements (promotors of recombination in E. coli) into yeast to test for their activity therein. Other promoters of recombination, specific to yeast, will be sought by conducting crosses in yeast between lambda plasmids containing fragments of yeast DNA.